In recent years, a telephone exchange system has a function of forwarding an incoming call to a predetermined telephone number to another telephone terminal in a manner set in advance.
Related art is disclosed in, for example, Patent Document 1. In Patent Document 1, there is disclosed a technology relating to a telephone exchange for forwarding an incoming call to another telephone set (number) in advance. Further, in the above-mentioned document, there is disclosed, as a secretarial function, a mechanism in which a relationship between a main telephone set and a sub-telephone set is registered in advance in the telephone exchange, to thereby call the sub-telephone set in response to a call to the number of the main telephone set. Further, there is disclosed a mechanism that facilitates a confirmation of presence/absence of a missed incoming call to the main telephone set and a connection to the sub-telephone set.
Further, in Patent Document 2, there is disclosed a mechanism of the telephone exchange system capable of discriminating which telephone terminal (number) an incoming call emitting sound is addressed to by a telephone set (proxy response source terminal) for conducting a proxy response as a part of a proxy response function so as to suit the secretarial function or the like. Specifically, there is disclosed a mechanism that provides, when a private branch exchange (PBX) causes a given telephone terminal to emit sound, display indicating a proxy response destination terminal to the telephone terminal to be caused to emit sound in a case where the incoming call is addressed to the proxy response destination terminal (number).